\documentclass{article}
\usepackage{pgfplots}
\begin{document}
\begin{tikzpicture}
\begin{axis}
  [symbolic y coords={a small bar,a medium bar,a large bar},
   ytick=data,
   xbar,
   y=0.7cm,
   enlarge y limits={abs=0.5cm},
  ]
  \addplot[fill=blue] coordinates
    {(42,a small bar)
     (50,a medium bar)
     (80,a large bar)
    };
\end{axis}
\end{tikzpicture}
\end{document}
